How should the rated load of a chain hoist be calibrated?

How should the rated load of a Chain Hoist be calibrated?

Chain hoists are a type of lifting equipment widely used in the industrial field. The accurate calibration of their rated loads is directly related to the safety, reliability and service life of the equipment. The following is a detailed introduction to the rated load calibration of chain hoists:

Calibration basis and standards
Industry standards: In China, the rated load calibration of chain hoists is mainly based on the mechanical industry standard JB/T 7334-2016 "Chain Hoists" and the group standard T/ZZB 0724-2018 "Chain Hoists". These standards clearly define the rated lifting weight range, corresponding working level, basic parameters, various test methods and inspection rules of chain hoists, etc., providing detailed technical basis for the calibration of rated loads.
Enterprise standards: Some large chain hoist manufacturers will also formulate enterprise standards based on their own production processes and quality control systems. These enterprise standards are usually higher than or equal to industry standards to ensure the competitiveness of products in the market and the safety of users.

Theoretical calculation method
Calculation based on material strength: The material strength of the main load-bearing parts of the hand chain hoist, such as hooks, chains, wall panels, etc., is an important factor in determining the rated load. It is necessary to first determine the mechanical performance indicators of the material, such as tensile strength and yield strength, and then calculate the maximum load that the hand chain hoist can bear, that is, the rated load, based on these indicators and the cross-sectional area and structural form of the components, under the premise of ensuring material safety, through mechanical formulas.
Calculation based on structural form and transmission efficiency: Hand chain hoists of different structural forms have different transmission efficiency and force distribution. For example, a hand chain hoist driven by an involute spur gear needs to consider the gear module, number of teeth, transmission ratio and other parameters, as well as factors such as friction loss during the transmission process. By establishing a mechanical model and a transmission model, the rated lifting capacity that can be achieved under a certain hand pull force is calculated.

Test calibration method
Static load test: Install the hand chain hoist on the test bench, gradually load it to 1.25 times the rated load, keep it for a period of time, and observe whether the hoist has abnormal conditions such as permanent deformation and cracks, and whether the parts are well matched and the connection is reliable. If the hand chain hoist does not have any abnormality within the specified load and time, it is considered that its rated load calibration is qualified.
Dynamic load test: Simulate the actual working conditions of the hand chain hoist, and perform lifting, running and other operations with 1.1 times the rated load. The number of tests is usually not less than 2000 times. During the test, check the running stability of the hoist, the meshing of the chain and the sprocket, the braking performance of the brake, etc. If the hand chain hoist can work normally during the test, without problems such as chain jamming, chain climbing, and brake failure, it means that the calibration of its rated load can meet the actual use requirements.
Fatigue test: Apply a certain amplitude of cyclic load to the hand chain hoist, and observe whether it will suffer fatigue damage after a large number of cycles. Fatigue tests can determine the load-bearing capacity of hand chain hoists during long-term use, so as to more accurately calibrate their rated loads to ensure the safety of the equipment throughout its service life.
Electrical measurement method: First, the hand chain hoist tension electrical measurement equipment should be calibrated, and then the rated lifting weight load should be hung on the hand chain hoist to be tested. During the lifting operation, the average hand pulling force of the lifting sprocket during the rotation of a flat slot and a vertical slot is measured. According to the relationship between the hand pulling force and the rated load, it is judged whether the rated load calibration is accurate.

Precautions in actual operation
Consider the safety factor: When calibrating the rated load, the safety factor must be fully considered. The determination of the safety factor should comprehensively consider the use environment, work level, importance and other factors of the hand chain hoist. Generally speaking, for heavy-loaded and frequently used hand chain hoists, the safety factor should be relatively large; while for light-loaded and infrequently used hand chain hoists, the safety factor can be appropriately reduced, but it must meet the minimum requirements of relevant standards.
Influence of environmental factors: The working environment temperature, humidity, corrosiveness and other factors of the hand chain hoist will also affect its rated load. For example, in an environment with high temperature, high humidity or corrosive gas, the strength and performance of the material will decrease, so it is necessary to appropriately reduce the rated load or take corresponding protective measures to ensure the safe operation of the equipment.
Manufacturing process and quality control: The quality of the manufacturing process and the strictness of quality control directly affect the actual load-bearing capacity of the hand chain hoist. If there are welding defects, insufficient processing accuracy, unstable material quality and other problems in the manufacturing process, the actual strength of the hand chain hoist may be lower than the design value, thereby affecting the calibration accuracy of the rated load. Therefore, it is necessary to strengthen the quality control of the manufacturing process to ensure that the quality of the hand chain hoist meets the standard requirements.

Verification and adjustment after calibration
User feedback and actual use verification: After the hand chain hoist is put into use, collect user feedback and data in actual use, such as lifting weight, frequency of use, fault conditions, etc., and compare and analyze them with the rated load calibration results. If problems such as frequent overload use or shortened equipment life are found, the rated load should be re-evaluated and adjusted in time.
Regular inspection and calibration: In order to ensure the continued accuracy of the rated load calibration of the hand chain hoist, it should be inspected and calibrated regularly. Inspection agencies can use the above test method to conduct sampling inspections on hand chain hoists in use, and confirm or adjust the rated load of the hand chain hoists based on the test results to ensure that they are always in a safe and reliable working condition.